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Torx (six-lobe, or hexalobular) sizes from T1 to T100, with the point-to-point dimension of the recess in millimetres, the metric screw each size is normally paired with and the torque the drive is rated for. The T-number is a designation, not a measurement: a T25 recess measures 4.5 mm point to point, a T20 measures 3.95 mm and a T30 measures 5.6 mm. The six-lobe drive spreads load over more contact area than a hex or cross head, which is why it resists cam-out and is used widely in automotive and electronics assembly.
| Torx size |
Point-to-point A (mm) |
Typical metric screw |
Maximum torque range (Nm) |
Typical use |
| T1 | 0.9 | - | 0.02 to 0.03 | - |
| T2 | 1 | - | 0.07 to 0.09 | - |
| T3 | 1.2 | - | 0.14 to 0.18 | - |
| T4 | 1.35 | - | 0.22 to 0.28 | - |
| T5 | 1.5 | - | 0.43 to 0.51 | - |
| T6 | 1.75 | M2 | 0.75 to 0.9 | Small electronics, laptop screws |
| T7 | 2.1 | - | 1.4 to 1.7 | Phones, cameras |
| T8 | 2.4 | M2.5 | 2.2 to 2.6 | Laptops, hard drives |
| T9 | 2.6 | - | 2.8 to 3.4 | Electronics |
| T10 | 2.8 | M3 | 3.7 to 4.5 | Electronics, small appliances |
| T15 | 3.35 | - | 6.4 to 7.7 | Appliances, automotive trim |
| T20 | 3.95 | M4 | 10.5 to 12.7 | Automotive interior, machinery covers |
| T25 | 4.5 | M5 | 15.9 to 19 | Automotive, garden machinery |
| T27 | 5.1 | - | 22.5 to 26.9 | Automotive engine, brackets |
| T30 | 5.6 | M6 | 31.1 to 37.4 | Automotive suspension, machinery |
| T40 | 6.75 | - | 54.1 to 65.1 | Automotive, heavy brackets |
| T45 | 7.93 | M8 | 86 to 103.2 | Heavy machinery, structural |
| T50 | 8.95 | M10 | 132 to 158 | Heavy machinery, suspension |
| T55 | 11.35 | - | - | Construction plant, heavy structural |
| T60 | 13.45 | - | - | - |
| T70 | 15.7 | - | - | - |
| T80 | 17.75 | - | - | - |
| T90 | 20.2 | - | - | - |
| T100 | 22.4 | - | - | - |
How to identify a Torx size
If the bit isn't marked, measure point to point across two opposite lobes of the recess in the screw head with calipers and match it to the table: 4.5 mm is a T25. Going one size too small cams out and rounds the lobes; one size too large won't enter. The most-used sizes in general repair are T20, T25 and T30, which cover most automotive interior and underbonnet fasteners.
Why a Torx bit measures smaller than the chart
The table gives dimension A from ISO 10664, which is the size of the recess in the screw. A driver bit has to enter that recess, so it is made slightly smaller. Measured across its lobes a T25 bit is about 4.39 mm against 4.5 mm for the recess, a T20 bit is about 3.84 mm against 3.95 mm, and a T30 bit is about 5.49 mm against 5.6 mm. If you are measuring a bit and not a screw, expect a figure a little under the chart value for the same size.
Security Torx and external Torx
Security Torx (Torx TR, also called pin-in Torx) has a pin in the centre of the recess and needs a driver with a matching hole, written as T10H, T20H and so on. A standard Torx bit won't seat in a security Torx screw. External Torx (E-Torx) is the inverse, a star-shaped socket that fits over an external lobed head. E sizes use their own numbering and are not interchangeable with the internal T-series.
Related standards
- ISO 10664 - Hexalobular internal driving feature for bolts and screws
- ISO 14579 and ISO 14580 - Hexalobular socket head cap screws and cheese head screws
- Torx and Torx Plus are trademarks of Acument Intellectual Properties
References
- ISO 10664:2014 - Hexalobular internal driving feature for bolts and screws
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